This is a small question.
If I post a question and discover later that the question was addressed, considered, or asked on MO or in some other forum, should I update my question with a cross-reference?
My instinct is that once I discover the antecedent I have a responsibility to include that in my question, but perhaps that's too strong?
A similar question could be asked about answers. If I answer a question and it turns out my answer is some variant of a previously published idea, do I have a responsibility to note this if I later find out?
Again my instinct is that the answer is 'yes' but I don't recall having seen this discussed here and it's not quite the same as knowing at the time of posting that the answer exists (and then I think it's clear-cut).